1. Field of the Invention
The present invention relates generally to a transverse stretching apparatus for stretching a film such as a resin film, or the like, to a predetermined width. More particularly, the present invention is an oven including a nozzle module for allowing a film to be subjected to heat treatment by blowing hot air toward the film from above and below.
2. Description of the Related Art
A transverse stretching apparatus is generally constructed such that the opposite ends of a film to be transversely stretched are captured by a conveyor and the film is then subjected to a series of treatments including preheating, stretching, thermal curing and cooling, while moving through an oven, until a predetermined width is obtained.
The oven includes a single nozzle module or a plurality of nozzle modules in each treatment region so that a film is heated up to a predetermined temperature. A typical conventional oven of the aforementioned type is disclosed in Japanese Laid-Open Patent No. 273825/1987. Specifically, the oven is constructed such that an opposing pair of air chambers, each including a radiator, are arranged on the opposite sides of a film passage and a plurality of nozzle units each having an upper nozzle for blowing a hot air over the entire width of a film from above and a lower nozzle, arranged opposite to the upper nozzle, for blowing a hot air over the entire width of the film from below, are alternately connected to the air chambers to constitute a nozzle module.
With the conventional oven constructed in the above-described manner, hot air is distributively supplied from the air chambers and flows in the upper and lower nozzles of adjacent nozzle units in the opposite direction, thus a slight temperature gradient appears in the upper nozzle across the whole width of the film and a slight temperature gradient appears in the lower nozzle across the whole width of the same so as to substantially cancel each other out. Consequently, the appearance of a temperature gradient over the whole nozzle module is suppressed, whereby temperature distribution becomes uniform across the entire width of the film passage. However, since the radiators are arranged on the film passage side of the air chamber while extending in parallel with the film passage, the base end side of each nozzle must have a stepped configuration in order to avoid any interference with the radiator and to assure that the upper and lower nozzles of each nozzle unit are connected to the air chambers with a predetermined distance therebetween. Thus, the geometrical structure of each nozzle is very complicated.
In addition, with respect to the conventional oven, the front nozzle unit can be opened in the forward direction, while the rear nozzle unit can be opened in the rearward direction. However, since the intermediate nozzle unit is fixedly secured to the air chambers, a sufficiently wide working space cannot be reserved for an operator to perform inspection, maintenance service, removal of a broken film or cleaning of the oven. Accordingly, these services are difficult to perform.